Japanese Patent Publication 3-64280 and U.S. Pat. No. 2,939,443 disclose patterning for irregularly shaped sheet materials, such as leather. These shapes are determined and inputted using a digitizer or the like, and a place having a defect is marked inside the image of the leather on a screen. Then, the parts to be patterned are positioned inside the leather image so as to avoid the defect, the leather is cut in accordance with the positioning of the parts, and the parts are removed.
However, since an ordinary patterning apparatus is used to cut a rectangular cloth or the like, it is not designed for patterning irregular shapes other than a rectangle. Accordingly, for example, adding a single layer image depicting the shape of a sheet material is likely to cause an error if a part is protruding outside the sheet material layer. However, a patterning apparatus is originally designed to closely position parts inside a rectangular shape, and just adding a layer will simply cause a string of errors, with no guarantee that it will be possible to position parts inside the sheet material.